mm: move vma_shrink(), vma_expand() to internal header

The vma_shrink() and vma_expand() functions are internal VMA manipulation
functions which we ought to abstract for use outside of memory management
code.

To achieve this, we replace shift_arg_pages() in fs/exec.c with an
invocation of a new relocate_vma_down() function implemented in mm/mmap.c,
which enables us to also move move_page_tables() and vma_iter_prev_range()
to internal.h.

The purpose of doing this is to isolate key VMA manipulation functions in
order that we can both abstract them and later render them easily
testable.

Link: https://lkml.kernel.org/r/3cfcd9ec433e032a85f636fdc0d7d98fafbd19c5.1722251717.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Gow <davidgow@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Kees Cook <kees@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Rae Moar <rmoar@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 6 insertions, 75 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 50e76cc633c4..9009e2b2805e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -712,80 +712,6 @@ static int copy_strings_kernel(int argc, const char *const *argv,
 #ifdef CONFIG_MMU
 
 /*
- * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
- * the binfmt code determines where the new stack should reside, we shift it to
- * its final location.  The process proceeds as follows:
- *
- * 1) Use shift to calculate the new vma endpoints.
- * 2) Extend vma to cover both the old and new ranges.  This ensures the
- *    arguments passed to subsequent functions are consistent.
- * 3) Move vma's page tables to the new range.
- * 4) Free up any cleared pgd range.
- * 5) Shrink the vma to cover only the new range.
- */
-static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	unsigned long old_start = vma->vm_start;
-	unsigned long old_end = vma->vm_end;
-	unsigned long length = old_end - old_start;
-	unsigned long new_start = old_start - shift;
-	unsigned long new_end = old_end - shift;
-	VMA_ITERATOR(vmi, mm, new_start);
-	struct vm_area_struct *next;
-	struct mmu_gather tlb;
-
-	BUG_ON(new_start > new_end);
-
-	/*
-	 * ensure there are no vmas between where we want to go
-	 * and where we are
-	 */
-	if (vma != vma_next(&vmi))
-		return -EFAULT;
-
-	vma_iter_prev_range(&vmi);
-	/*
-	 * cover the whole range: [new_start, old_end)
-	 */
-	if (vma_expand(&vmi, vma, new_start, old_end, vma->vm_pgoff, NULL))
-		return -ENOMEM;
-
-	/*
-	 * move the page tables downwards, on failure we rely on
-	 * process cleanup to remove whatever mess we made.
-	 */
-	if (length != move_page_tables(vma, old_start,
-				       vma, new_start, length, false, true))
-		return -ENOMEM;
-
-	lru_add_drain();
-	tlb_gather_mmu(&tlb, mm);
-	next = vma_next(&vmi);
-	if (new_end > old_start) {
-		/*
-		 * when the old and new regions overlap clear from new_end.
-		 */
-		free_pgd_range(&tlb, new_end, old_end, new_end,
-			next ? next->vm_start : USER_PGTABLES_CEILING);
-	} else {
-		/*
-		 * otherwise, clean from old_start; this is done to not touch
-		 * the address space in [new_end, old_start) some architectures
-		 * have constraints on va-space that make this illegal (IA64) -
-		 * for the others its just a little faster.
-		 */
-		free_pgd_range(&tlb, old_start, old_end, new_end,
-			next ? next->vm_start : USER_PGTABLES_CEILING);
-	}
-	tlb_finish_mmu(&tlb);
-
-	vma_prev(&vmi);
-	/* Shrink the vma to just the new range */
-	return vma_shrink(&vmi, vma, new_start, new_end, vma->vm_pgoff);
-}
-
-/*
  * Finalizes the stack vm_area_struct. The flags and permissions are updated,
  * the stack is optionally relocated, and some extra space is added.
  */
@@ -877,7 +803,12 @@ int setup_arg_pages(struct linux_binprm *bprm,
 
 	/* Move stack pages down in memory. */
 	if (stack_shift) {
-		ret = shift_arg_pages(vma, stack_shift);
+		/*
+		 * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
+		 * the binfmt code determines where the new stack should reside, we shift it to
+		 * its final location.
+		 */
+		ret = relocate_vma_down(vma, stack_shift);
 		if (ret)
 			goto out_unlock;
 	}